The knowledge content related to triangles is one of the core and most important contents in the field of mathematics and geometry learning in junior middle schools, because triangles are not only one of the basic plane graphics, but also the tools and foundation for learning other graphics. If you want to learn quadrilateral well, you must first master the knowledge of triangle, otherwise you will find quadrilateral difficult to learn after one semester.

Triangle, as the basic figure in plane geometry, can be said that only by learning triangles well can we learn geometry well. For example, the properties of triangles are the basis of learning and studying polygons;

The congruence of two triangles explores the shape and size of two figures to prepare for further study of triangle similarity;

The nature and judgment of special triangles (isosceles triangles and equilateral triangles) is an important tool for continuing to learn special quadrangles and trigonometric functions.

Most problems about geometric figures can eventually be transformed into triangular problems, which can be solved by using the knowledge of triangles.

A careful study of the mathematics test questions in the senior high school entrance examination in recent years all over the country shows that the triangle-related senior high school entrance examination questions occupy a certain proportion. The senior high school entrance examination will not only pay attention to basic knowledge and skills when examining triangles, but also highlight the examination of hands-on operation ability and innovation consciousness in some comprehensive questions. So when reviewing triangles, we must strengthen the accumulation of knowledge and methods.

Mathematics curriculum standards put forward some requirements for junior high school students to master geometry, such as allowing students to explore the basic properties of basic graphics (straight lines and circles) and their relationships, further enriching their understanding and feelings of spatial graphics, learning the basic properties of translation, rotation and symmetry, appreciating and experiencing the wide application of transformation in real life, learning the method of determining the position of objects by using coordinate system, developing spatial concepts and so on.

Therefore, some triangle senior high school entrance examination questions will prove some basic properties of triangles from students' practical experience and graphic properties, so as to understand the necessity of proof, understand the basic process of proof, master the format of comprehensive proof, and initially feel the axiomatic thought.